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Zinc absorption in premature infants: comparison of two isotopic methods
J K Friel1, W L Andrews, B S Simmons
1Department of Biochemistry, Memorial University of Newfoundland, St.John's, Canada.
Insights
Measuring zinc absorption in premature infants using urine isotopes is feasible. This method, utilizing double isotopic enrichment, offers a less invasive alternative to fecal collection for assessing zinc status in very-low-birth-weight infants.
Area of Science:
- Pediatric Nutrition
- Trace Element Metabolism
- Neonatal Physiology
Background:
- Accurate assessment of zinc absorption is crucial for very-low-birth-weight (VLBW) premature infants.
- Traditional methods using fecal collection are challenging and often incomplete in this population.
- Isotope dilution techniques offer a potential alternative for measuring zinc absorption.
Purpose of the Study:
- To evaluate the feasibility of using urinary double isotopic enrichment to determine fractional zinc absorption in VLBW premature infants.
- To compare fractional zinc absorption calculated from urine with that calculated from fecal excretion.
- To assess endogenous fecal zinc (EFZ) and net zinc absorption and retention in this cohort.
Main Methods:
- A simultaneous oral (68Zn) and intravenous (70Zn) isotope administration was used in VLBW infants.
- Urine and fecal samples were collected and analyzed using inductively coupled plasma mass spectrometry.
- Fractional absorption was calculated from urinary isotopic enrichment and compared to fecal measurements.
Main Results:
- Mean fractional zinc absorption calculated from urine was 0.22 ± 0.09, closely matching the fecal value of 0.25 ± 0.07.
- Endogenous fecal zinc (EFZ) showed significant variability, averaging 390 ± 270 µg.kg(-1).d(-1).
- Urinary zinc excretion was significantly lower than fecal excretion, highlighting the challenges of fecal sample collection.
Conclusions:
- Urinary double isotopic enrichment is a viable and less invasive method for assessing fractional zinc absorption in VLBW premature infants.
- This method may replace difficult and often incomplete fecal collection in studies of zinc metabolism in neonates.
- Accurate zinc absorption data is vital for optimizing nutritional support and growth in premature infants.
Abstract:
The fractional absorption of an oral dose of zinc can be measured in adults when given simultaneously with an intravenous dose and subsequently measuring the ratio of the double isotopic enrichment of urine. To test this method in very-low-birth-weight (VLBW) premature infants [n=5 females and 7 males, 1160 +/- 290 g (chi +/- SD) birth weight, 29 +/- 4 wk gestational age], an oral dose of either 300 or 1200 micrograms 68Zn.kg(-1).d(-1) was equilibrated with formula or human milk and administered simultaneously with either 50 or 100 micrograms 70Zn.kg(-1).d(-1) given intravenously 35 +/- 3 wk postconception. Urine and fecal samples were collected for 3-6 d and analyzed by inductively coupled plasma mass spectrometry. Endogenous fecal zinc (EFZ) was determined from isotopic enrichment, whereas net absorption and retention were calculated by traditional methods. The mean fractional absorption calculated from urine was 0.22 +/- 0.09 and from feces it was 0.25 +/- 0.07. Zinc intake averaged 1821 +/- 330, fecal excretion 1637 +/- 419, and urinary excretion 67 +/- 30 micrograms.kg(-1).d(-1). EFZ averaged 390 +/- 270 micrograms.kg(-1).d(-1) and ranged from 48 to 889 micrograms.kg(-1).d(-1). Net absorption was 220 +/- 316 micrograms.kg(-1).d(-1) and net retention was 131 +/- 334 micrograms.kg(-1).d(-1). True absorption was 373 +/- 161 micrograms.kg(-1).d(-1). Fecal collection is difficult, tedious, and often incomplete, and may be replaced by urine collection for the fractional absorption of zinc in groups of premature infants.